Conventional portland cement is widely used in making concrete for structural uses and for producing pavements such as road surfaces, sidewalks and the like. Portland cement is generally in the form of a finely divided gray powder which is made by grinding portland cement clinker to a high degree of fineness. Portland cement clinker is generally made by intensely heating a mixture of pulverized limestone and certain types of pulverized clay until incipient fusion of the pulverized mixture occurs, whereupon the resulting product is cooled to form the portland cement clinker. A special rotary furnace is generally used to heat the mixture.
Concrete is generally made by producing a mixture of portland cement, sand, gravel or other aggregate, and water. In the hardening of concrete, the water reacts and combines with the portland cement. Any excess water evaporates.
Concrete sets or solidifies in a matter of hours, but the full ultimate strength of the concrete develops slowly over a longer period, such as 28 days, for example. Special grades of portland cement are available to produce high early strength in the concrete. Such special grades of portland cement are generally ground to an especially high degree of fineness.